1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus using the zoom lens. The zoom lens is particularly suitable for use in an image pickup optical system of video cameras, digital cameras, monitoring cameras, television cameras, and the like.
2. Description of the Related Art
As semiconductor and mechanical manufacturing technologies continue to improve, image pickup apparatuses such as video cameras, digital still cameras, broadcast cameras, and monitoring cameras that use solid-state image pickup devices, and silver-halide film cameras that use silver-based film are being manufactured in reduced size. As image pickup optical systems used for these image pickup apparatuses, there is a need for zoom lenses featuring a shorter total lens length (distance between a first lens surface and an image plane), reduced size, a higher zoom ratio, a higher resolving power, among other requirements.
As an example of a type of zoom lenses that satisfy some of these demands, a five-unit zoom lens is known. The five-unit zoom lens includes first to fifth lens units arranged sequentially in order from the object side to the image side of the zoom lens. The first lens unit has a positive refractive power, the second lens unit has a negative refractive power, the third lens unit has a positive refractive power, the fourth lens unit has a negative refractive power, and the fifth lens unit has a positive refractive power. These lens units are moved to perform zooming.
In general, a compact zoom lens, the size of which decreases with increasing zoom ratio, may be achieved by decreasing the number of lens elements included in each lens unit, increasing the refractive power of a main magnification varying lens unit, and by increasing the movement amount of the main magnification varying lens unit during zooming. By decreasing the number of lens elements in each lens unit and increasing the refractive power and the movement amount of the main magnification varying lens unit, a higher zoom ratio may be easily obtained. However, aberration fluctuation during zooming is increased, and accordingly, high optical performance over the entire zoom range is difficult to maintain.
In the above-described five-unit zoom lens, in order to reduce the size of the entire lens system, obtain a high zoom ratio, and achieve good optical performance, it is important to appropriately set a lens configuration and the refractive power of each lens unit, movement conditions of each lens unit for zooming, and the like.
Japanese Patent Laid-Open No. 1-241513 and U.S. Pat. No. 7,450,314 disclose zoom lenses, in which first and second lens units each include two lens elements, thereby reducing the sizes of lens units. The zoom ratio of the zoom lens disclosed in Japanese Patent Laid-Open No. 1-241513 is about 1.9, and the zoom ratio of the zoom lens disclosed in U.S. Pat. No. 7,450,314 is about 4.8 to 4.9. These zoom ratios may be insufficient to satisfy the above-outlined requirements of a modern zoom lens. Furthermore, an image-taking angle of view of the zoom lens disclosed in U.S. Pat. No. 7,450,314 is about 23.8 degrees at the wide-angle end. These image-taking angles of view may be insufficient.
The present invention provides a zoom lens that features a high zoom ratio and a wide angle of view, has a short total lens length, and achieves high optical performance over the entire zoom range. The present invention also provides an image pickup apparatus equipped with a zoom lens having the above characteristics.